THE SINUS MAXILLARIS 



The sinus maxillaris is the most constant of the nasal 

 accessory sinuses. Reschreiter mentions reports of four 

 cases in which a sinus maxillaris was absent. We have 

 found no other instances in which complete failure of its 

 development has been recorded. The extent of its develop- 

 ment is also more regular than that of any of the other 

 sinuses, as was shown by comparing the tables of measure- 

 ments given by the various observers. 



In embryos eighty-five days old there is a lateral out- 

 pouching of mucosa, demonstrable in the inferolateral por- 

 tion of the wall of the infundibulum ethmoidale, slightly 

 anterior to its midpoint anteroposteriorly. This is the 

 primitive sinus maxillaris, which gradually develops as an 

 oblong recess, extending first into the lateral nasal capsule, 

 after the resorption of which it continues its advance and 

 development into the maxilla. The point of primary lat- 

 eral pouching persists as the ostium maxillare. 



As the expansion in the maxilla increases anteroposteriorly 

 much more rapidly than does the diameter of the ostium, 

 there is thus developed a medial wall, which, by the latter 

 part of the sixth or early in the seventh fetal month, is 

 sufficient to make the outline of the pouching demonstrable 

 as an oblong sinus. The relatively small vertical diameters 

 of fetal and infantile maxillae and the close approximation 

 of the developing teeth to the orbital floor preclude the 

 possibility of a rapid increase in the vertical and lateral 



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